Composition Dependencies of the Rheological Properties of Rice Starch Blends

Abstract

Cereal Chem. 81(2):267-274The gelatinization, pasting, and dynamic rheological parameters of rice starch dispersions from Kaoshiung Sen 7 (KSS7), Taichung Waxy 70 (TCW70), and their blends were examined in relation to total starch concentration (C t ) and the property of starch components. Mixing the rice starches, especially at equivalent ratios, resulted in decreasing onset temperature for gelatinization or developing viscosity and in cold-paste viscosity, accompanied by a synergistically increased peak viscosity. The logarithmic of storage moduli, G′, for all starch dispersions except the retrograded systems of C t = 20−30 wt%, showed two linear dependencies on the weight-average amylose content (AC) of the blends separating at a critical AC of 20 wt% (i.e., TCW70 = 25 wt%). Interestingly, the temperatures at which G′ started to increase drastically maximized on heating, and the exponent n of G′ ∝ C t n also maximized at the same TCW70 starch concentration. Generally, the elasticity of the systems after complete gelatinization and retrogradation followed the isostress models of Takayanagi's blending laws at C t = 10 wt%, but changed to the intermediates of isostress and isostrain at C t = 20−30 wt%. The changes in these parameters can be explained by competitive swelling behavior, the strengthening effect of swollen granules, and shear disintegration.

Starch blends and their physicochemical properties

“…However, when the peak viscosity of the blend was lower than expected, it was not always the starch with the highest peak viscosity that was present in the smallest portion . Only for blends of regular and waxy rice starches, non‐additive behavior was maximal when starches were present in equal portions .…”

“…However, probably not only differences in gelatinization temperature, but also in granule size and rate of water absorption impact the gelatinization properties. Additive effects were observed for blends of regular and waxy rice starches .…”

“…Nevertheless, based on the gelatinization enthalpy values, it has still been suggested that gelatinization occurs independently . This has been the case for blends of maize and cassava starches , maize and yam starches , potato and barley starches , HMT potato and amaranth starches , cassava and lima bean starches , rice starches with different amylose contents , canna and rice starches , canna and mung bean starches and maize and potato starches (Table ). Although for a canna – rice starch blend gelatinization behavior appeared to be additive, based on the gelatinization temperatures of the blend, it was suggested that both starches influenced each other's gelatinization behavior due to the large difference in their granule sizes (Table ) .…”

“…Blending different starches increases the complexity of the system and makes the interpretation of analytical results even more challenging. The starch concentration in the different studies varies from 6 to 12% and all available studies compare pasting properties of the blends and the individual starches at the same total starch concentration .…”

“…However, in blends containing starches with similar granule size, other factors are involved. For blends of regular and waxy rice starches, both a reduction in peak viscosity (one blend, with a regular rice starch with an amylose content of 17% ) and an increase in peak viscosity (three blends of waxy rice starch always with a different regular rice starch with an amylose content of 23% or higher ) have been recorded. It seems that the amylose content and swelling power of regular rice starch play a role in determining the non‐additive behavior.…”